I often see all sorts of batteries in Spitfires, many of them being wrong. Anything from truck size to lawn mower size. The following is a rundown of what is correct.
There are two (2) different size batteries for Spitfires, large for MKI, MKII & MK3 when using a generator and small for MKIV & 1500 which have an alternator. If you have converted your early model Spitfire to an alternator then there is no point in using the large and heavy battery.
The small battery weights about 11 kgs and the large battery weighs about 15 kgs. The length and height of both batteries is the same 230mm & 190mm it is the width that is different 135mm for the small and 170mm for the large.
Exide batteries are the largest manufacturer of automotive batteries in Australia and therefore probably the more common, so I will quote the identification or model number for Exide batteries or sometimes know as Champion batteries. The large battery for the early Spitfire with a generator is N50 and the small battery for the later model Spitfires with an alternator is P310D.